What kind of car do you have? Some use fiberglass packing in the muffler (like my Volvo), and it’s not unheard of for it to come out of the exhaust when you’re experiencing problems. If the string like stuff looks like strands of hair, that could be it.

Can you describe the stuff in more detail? Nothing stringy should be coming out of the exhaust. Since I have no idea what it is, I can’t say if it could be dangerous or not. Have someone check it out in person if you have any doubts.

It’s possible, but it may not be legal. A “straight pipe” typically refers to an exhaust with no catalytic converters, resonators, or mufflers. In this case it sounds like your friend just deleted the catalytic converter(s). Check your local emissions laws to see if this is allowed. If you have to take a smog test, you will almost certainly fail without catalytic converters.

I’m not sure if this is related to the misfires or not. Is your car throwing any codes?